Sparse code multiple access (SCMA for short) is a new multiple access manner. In this multiple access manner, multiple users use a same resource block (RB for short). Each resource block includes several resource elements (RE for short). One RE may be a subcarrier-symbol resource element in an orthogonal frequency division multiplexing (OFDM for short) technology, or may be a time-frequency resource element in another air interface technology. A communications system that uses the SCMA access manner may be referred to as an SCMA system.
A codebook is an important resource that needs to be used in data communication. A single codebook generally includes multiple codewords, and multiple codebooks may be used at the same time. In a conventional communications system, such as an SCMA system, powers of multiple codebooks used at the same time are equal. When decoding a received signal, a conventional receiver (the receiver may be a base station or a user terminal) references all possible codebooks at the same time. Because powers of all the possible codebooks referenced at the same time are equal, decoding quality cannot be ensured. In addition, when there is a relatively large quantity of possible codebooks, complexity of a signal decoding operation at the receiver is relatively high. For example, when there are hundreds of possible codebooks, the complexity of the signal decoding operation at the receiver is extremely high.